Siemens EQ6 Error: "Let the unit cool down".

Hello
,I have an EQ6 S300 which throws the error "Let the unit cool down". The previous owner has already installed a new grinder. Because the message still existed, the machine went to the repair department, where a thermoswitch was changed. Afterwards the machine ran again (approx. 3 weeks) until the error
appeared
again
.

The machine starts, you hear a short buzzing sound and then the error message appears after about 5 seconds.

Does

anyone have an idea what it

could

be

?

Could it be that the pump is defective and that is why the flow heater overheats so quickly? Or what could trigger the error message so quickly? I also have no possibility to get into the menu. The display flashes where all drinks are passing through and at the end of the menu the

error message appears.

What do you think it could be?